A first aspect of the present invention relates generally to folded dipole antennas. A second aspect of the present invention relates to a coaxial to microstrip transition. A third aspect of the present invention relates to a retaining element. All aspects of the invention are typically but not exclusively for use in wireless mobile communications systems
U.S. Pat. No. 6,317,099 and U.S. Pat. No. 6,285,666 describe a folded dipole antenna with a ground plane; and a conductor having a microstrip feed section extending adjacent the ground plane and spaced therefrom by a dielectric, a radiator input section, and at least one radiating section integrally formed with the radiator input section and the feed section. The radiating section includes first and second ends, a fed dipole and a passive dipole, the fed dipole being connected to the radiator input section, the passive dipole being disposed in spaced relation to the fed dipole to form a gap, the passive dipole being shorted to the fed dipole at the first and second ends.
The radiating section is driven with a feed which is not completely balanced. An unbalanced feed can lead to unbalanced currents on the dipole arms which can cause beam skew in the plane of polarization (vertical pattern for a v-pol antenna, horizontal pattern for a h-pol antenna, vertical and horizontal patterns for a slant pol antenna), increased cross-polar isolation in the far field and increased coupling between polarizations for a dual polarized antenna.
A stripline folded dipole antenna is described in U.S. Pat. No. 5,917,456. A disadvantage of a stripline arrangement is that a pair of ground planes is required, resulting in additional expense and bulk.
U.S. Pat. No. 4,837,529 describes a microstrip to coaxial side-launch transition. A microstrip transmission line is provided on a first side of a ground plane, and a coaxial transmission line is provided on a second side of the ground plane opposite to the first side of the ground plane. The coaxial transmission line has a central conductor directly soldered to the microstrip line. Direct soldering to the microstrip line has a number of disadvantages. Firstly, the integrity of the joint cannot be guaranteed. Secondly, it is necessary to construct the microstrip line from a metal which allows the solder to flow. The coaxial cylindrical conductor sleeve is also directly soldered to the ground plane. Direct soldering to the ground plane has the disadvantages given above, and also the further disadvantage that the ground plane will act as a large heat sink, requiring a large amount of heat to be applied during soldering.
An exemplary embodiment provides in a first aspect a dual polarized folded dipole antenna comprising:
a first unit configured for transmitting and/or receiving signals in a first polarization direction; and
a second unit configured for transmitting and/or receiving signals in a second polarization direction different to the first polarization direction,
wherein each unit includes a conductor having a feed section, a radiator input section, and at least one radiating section integrally formed with the radiator input ,section and the feed section, the radiating section including first and second ends, a fed dipole and a passive dipole, the fed dipole being connected to the radiator input section, the passive dipole being disposed in spaced relation to the fed dipole to form a gap, the passive dipole being shorted to the fed dipole at the first and second ends.
The exemplary embodiment provides in a second aspect a folded dipole antenna comprising:
a ground plane
a conductor having a feed section extending adjacent the ground plane and spaced therefrom by a dielectric, a radiator input section, and at least one radiating section integrally formed with the radiator input section and the feed section, the radiating section including first and second ends, a fed dipole and a passive dipole, the fed dipole being connected to the radiator input section, the passive dipole being disposed in spaced relation to the fed dipole to form a gap, the passive dipole being shorted to the fed dipole at the first and second ends,
wherein the feed section is a microstrip feed section having an adjacent ground plane on one side only, and
wherein the radiator input section includes a balun transformer.
The balun transformer provides a balanced feed and obviates the problems discussed above.
The exemplary embodiment provides in a third aspect a folded dipole antenna comprising:
a ground plane
a conductor having a feed section extending adjacent the ground plane and spaced therefrom by a dielectric, a radiator input section, and at least one radiating section integrally formed with the radiator input section and the feed section, the radiating section including first and second ends, a fed dipole and a passive dipole, the fed dipole being connected to the radiator input section, the passive dipole being disposed in spaced relation to the fed dipole to form a gap, the passive dipole being shorted to the fed dipole at the first and second ends,
wherein the feed section is a microstrip feed section having an adjacent ground plane on one side only, and
wherein the radiator input section includes a splitter, first and second feedlines which meet said feed section at said splitter so as to complete a closed loop including the first and second feedlines and the radiating section, and a phase delay element for introducing a phase difference between the first and second feedlines.
The exemplary embodiment provides in a fourth aspect a coaxial to microstrip transition comprising:
a ground plane;
a microstrip transmission line on a first side of the ground plane;
a coaxial transmission line on a second side of the ground plane opposite to the first side of the ground plane, the coaxial transmission line having a central conductor coupled to the microstrip line, a coaxial cylindrical conductor sleeve coupled to the ground plane, and a dielectric material between the central conductor and the sleeve,
a conductive ground transition body in conductive engagement with the sleeve; and
a ground locking member applying a force to the ground transition body so as to force the ground transition body into conductive engagement with the ground plane.
This construction obviates the need for a direct solder joint between the sleeve and the ground plane.
The exemplary embodiment provides in a fifth aspect a coaxial to microstrip transition comprising:
a ground plane;
a microstrip transmission line on a first side of the ground plane;
a coaxial transmission line on a second side of the ground plane opposite to the first side of the ground plane, the coaxial transmission line having a central conductor coupled to the microstrip line, a coaxial cylindrical conductor sleeve coupled to the ground plane, and a dielectric material between the central conductor and the sleeve,
a conductive line transition body in conductive engagement with the central conductor; and
a line locking member applying a force to the line transition body so as to force the line transition body into conductive engagement with the microstrip line.
This construction obviates the need for a direct solder joint between the central conductor and the microstrip line.
The exemplary embodiment provides in a sixth aspect a method of constructing a coaxial to microstrip transition, the method comprising:
arranging a microstrip transmission line on a first side of a ground plane;
arranging a coaxial transmission line on a second side of the ground plane opposite to the first side of the ground plane, the coaxial transmission line having a central conductor coupled to the microstrip line, a coaxial cylindrical conductor sleeve coupled to the ground plane, and a dielectric material between the central conductor and the sleeve,
arranging a conductive ground transition body in conductive engagement with the sleeve; and
applying a force to the ground transition body so as to force the ground transition body into conductive engagement with the ground plane.
The exemplary embodiment provides in a seventh aspect a method of constructing a coaxial to microstrip transition, the method comprising:
arranging a microstrip transmission line on a first side of a ground plane;
arranging a coaxial transmission line on a second side of the ground plane opposite to the first side of the ground plane, the coaxial transmission line having a central conductor coupled to the microstrip line, a coaxial cylindrical conductor sleeve coupled to the ground plane, and a dielectric material between the central conductor and the sleeve,
arranging a conductive line transition body in conductive engagement with the central conductor; and
applying a force to the line transition body so as to force the line transition body into conductive engagement with the microstrip line.
The exemplary embodiment provides in an eighth aspect an electrically insulating retaining element for retaining together adjacent ends of a pair of dipoles, the element comprising a body portion having a pair of sockets on opposite side of the body portion; and a pair of resilient members which each obstruct a respective socket and resiliently flex, when in use, to admit an end of a dipole into the socket.
The exemplary embodiment provides in a ninth aspect a dipole assembly comprising two or more dipoles having adjacent ends retained together by electrically insulating retaining elements, each element comprising a body portion having a pair of sockets on opposite side of the body portion; and a pair of resilient members which each obstruct a respective socket and resiliently flex, when in use, to admit an end of a dipole into the socket.